Conventional sail booms, in particular mainsail booms, are designed straight, the sail being either guided and held in a jag with the entire under leech or held with a free under leech only on the mast side and at the boom yardarm. In order to obtain a flow-advantageous profile adapted to the wind, use is made of sails which are shaped from a broad range of materials so as to bulge three-dimensionally and are stiffened with preferably horizontal, but also with vertical sail battens, which are shaped in a broad range of manners, in such a way as to allow the rear setting of the sail to be increased in size as much as possible and as a result a larger sail area and thus a larger area exposed to the wind to be achieved in relation to the length of the fore leech and under leech.
As conventional manual sail reefing or stowing requires, above all in relatively large vessels, the exertion of a high degree of force, recent decades have seen a transition to mechanically rolling up the sails either into a hollow mast or into the hollow boom. This has the drawback that three-dimensionally profiled, bulging, i.e. aerodynamically advantageously cut, sails cannot be rolled up correctly on account of the partially different cloth lengths to be rolled up and, in the reefed, i.e. partly rolled-up, state, lose shape and have a poor position and thus poor sailing properties.
Flat-cut sails, such as are used as a remedy for roller reefing booms, also with horizontal sail battens which can be jointly rolled up, have, as a result of the straight under leech and on account of the flatness, an aerodynamically disadvantageous shape and thus, again, poorer sailing properties, above all in weak wind, where sails profiled in a bulging manner are necessary.
In recent decades, a number of developments have been proposed in order to improve the drawbacks of the poor position of the sail and thus the poor sailing properties.
These are exclusively improvements of the sail position of conventional manually reefable sails (jiffy reef) by devices which improve the curvature of the under leech in relation to a straight sail boom. For example “Boisson FR 2472508 and FR 2557064” in which the sail boom, along with the setting device according to the invention, disadvantageously has to be rotated through 180° during each tack, such as for example also in “Palmblad DE 371790”.
Further examples of evaluation of the prior art include: Darzinskis U.S. Pat. No. 4,261,276, Vicard FR 2199722, Larsson CH 615631. None of these cases solves existing sail position problems which occur in roller reefing installations and for which a solution will be provided hereinafter.